Sorry, that article might be premature. This feature was rolled out to some users for testing, but isn't generally available until Firefox 143 for Android. There is a way to turn it on yourself through the "Secret Settings" menu if you want to try it out now. Here's where you find that: menu button > Settings > About Firefox Tap the Firefox Logo 5 times to enable Debug mode. Firefox should display a message that is has been enabled. Back out to the menu and Secret Settings should now appear below About Firefox. Tap Secret Settings. Scroll down and near the bottom you'll find "Enable DNS over HTTPS settings". Tap the gray slider switch to turn it on. Back out to the menu, scroll up, and DNS over HTTPS should now be available. (I got that far, but didn't test whether modifying the settings works.)